Below are key operational considerations, common issues, and actionable solutions to ensure optimal performance and safety.
A frequent concern during transformer operation is unexpectedly low core-to-ground insulation resistance, which can undermine electrical safety and performance.
The most common trigger is high ambient humidity. Excessive moisture in the air penetrates the transformer’s insulation layers—including the core, high-voltage windings, and low-voltage windings—gradually reducing insulation resistance over time. This issue is particularly prevalent in damp environments, unventilated spaces, or after prolonged storage in humid conditions.
To resolve moisture-induced insulation degradation, targeted heat treatment is recommended:
Position iodine-tungsten lamps strategically beneath the low-voltage windings, ensuring uniform heat distribution across the core, high-voltage windings, and low-voltage windings. Conduct continuous baking for 12 hours. The controlled heat effectively evaporates trapped moisture within insulation materials, gradually restoring the insulation resistance to industry-accepted levels. For severe humidity-related issues, extend the baking duration or use multiple lamps to enhance heat coverage.
Zero insulation resistance between the core and ground indicates a direct metallic connection—an urgent issue that requires immediate troubleshooting to prevent short circuits or equipment failure.
This problem typically stems from unintended electrical continuity between the core and other metallic components, such as:
- Burrs on core laminations or clamps, or stray wires trapped during manufacturing, which pierce insulation layers.
- Overlapping metal ends between the core and structural clamps due to improper assembly.
- Damaged insulation on the transformer’s base feet, creating direct contact between the core and the frame.
- Foreign metallic objects (e.g., loose fasteners, debris) lodged in the low-voltage windings, bridging the core and pull plates.
- Initial Inspection: Use a multimeter to verify continuity between the core and ground, then conduct a thorough visual inspection of the core, windings, and structural components. Look for visible burrs, loose wires, damaged insulation, or foreign metallic debris.
- Base Foot Check: If no surface issues are found, inspect the insulation integrity of the transformer’s base feet. Replace damaged insulation pads if necessary.
- Controlled Electrical Pulse Method: If the issue persists, employ this targeted solution:
- Connect the ground terminal of an electric welding machine to the transformer’s grounding plate.
- Set the welding current to approximately 250A, then lightly tap the base feet with a welding electrode.
This controlled pulse breaks down unintended metallic bridges (e.g., microscopic burr connections) without damaging core or winding components, restoring proper insulation between the core and ground.
On-site power transmission is a critical phase that demands rigorous pre-checks to avoid operational hazards. While practices may vary (some stations conduct 3 test energizations, others 5), the following checklist ensures safety and reliability:
- Mechanical Integrity: Confirm all structural bolts, winding clamps, and terminal connections are securely tightened. Remove any residual metallic debris or foreign objects from the core and winding assembly.
- Insulation Clearances: Verify that electrical clearances between live components, between live parts and ground, and between high-voltage/low-voltage windings comply with IEC, ANSI, or local industry standards to prevent dielectric breakdown.
- Electrical Functionality: Test auxiliary systems (temperature controllers, cooling fans, protection relays) to ensure they respond correctly to simulated operating conditions.
- Wiring Accuracy: Cross-verify high-voltage and low-voltage wiring against the design schematic, ensuring phase sequence alignment and no cross-wiring errors.
- Insulation Compliance: Recheck insulation resistance (core-to-ground, winding-to-winding, winding-to-ground) with a megohmmeter to confirm values meet pre-commissioning thresholds.
- Pest Prevention: Seal cable entry points, ventilation openings, and enclosure gaps with mesh screens or weatherstripping to block small animals—their intrusion can cause short circuits or equipment damage.
- Drainage Check: Ensure drainage channels for the enclosure and floor plates are unobstructed to prevent water accumulation, which can degrade insulation over time.
Discharges (sparking or arcing) between the transformer’s aluminum alloy enclosure and installed floor plates during operation signal underlying conductivity or grounding issues.
This phenomenon occurs when electrical conductivity between enclosure panels is inadequate, or the grounding system is poorly implemented. Insulating paint, oxide layers, or debris on enclosure joint surfaces disrupt the flow of fault current to ground, creating voltage differences that manifest as discharges.
- Conductivity Restoration: Use a 2500V megohmmeter to identify areas of poor conductivity on the enclosure. Carefully break down insulating layers at these points (e.g., scrape off paint or oxide film) to establish electrical continuity between panels.
- Enhanced Grounding: Scrape the paint or oxide film at all enclosure joints (panel seams, mounting brackets, and connection points) to expose bare metal. Connect these points with copper conductors, then secure a reliable ground connection to the site’s main grounding system. This ensures efficient dissipation of fault current and eliminates discharge hazards.
By adhering to these guidelines, operators can address common operational issues, mitigate risks, and maximize the service life of dry-type epoxy resin cast transformers. Regular maintenance, combined with proactive troubleshooting, ensures consistent performance in diverse industrial, commercial, and infrastructure applications.
